It is generally recognized in this art that hydrothermal stability of the faujasite zeolites increases with increase in the SiO.sub.2 /Al.sub.2 O.sub.3 ratio. Thus the Y zeolites (See Breck U.S. Pat. No. 3,130,007) when incorporated in a matrix in catalytic cracking operations give higher conversions than similar catalysts produced from the X type faujasite zeolites. (See Milton U.S. Pat. No. 2,882,244 and Plank et al. U.S. Pat. Nos. 3,140,249 and 3,140,253).
It is a well known historical fact that when the Y zeolites became available the industry abandoned the X type as a catalyst precursor in favor of catalysts based on the Y zeolites.
Generally speaking the catalysts available to the industry prior to the introduction of the Y zeolites were based on a zeolite having a faujasite x-ray pattern of a faujasite zeolite of SiO.sub.2 /Al.sub.2 O.sub.3 ratio much below 3 which had been exchanged with monovalent cations such as hydrogen or ammonium NH.sub.4 or polyvalent cations such as rare earth or rare earth and magnesium cations. These were incorporated in matrixes which included clays, hydrated alumina, silica sols and silica gels and silica-alumina gels.
Catalytic activity of such catalysts are reported in terms of activity as measured by a test procedure which has been widely accepted. It is of the type reported in the Oil and Gas Journal issues of 1966, Volume 64, Number 39, Pages 84, 85 as modified as reported in the issue of Nov. 22, 1971, Pages 60-63. In the following examples the conditions were as follows. The calcined catalyst was first steamed at temperatures and times specified below and then used in cracking of a petroleum fraction under the following conditions. Oil charge was a wide boiling range high sulfur feed stock (boiling range about 430.degree. to 1000.degree. F.). The catalyst to oil ratio equals 2.92. The weight hourly space velocity equals 16.45 grams of oil per gram of catalyst per hour. The temperature of the reactor is 910.degree.. The percent conversion is reported as the volume of liquid condensate product of boiling point range of up to 421.degree. F. based on the volume of liquid charge. The percent conversion after calcined in air three hours at 1050.degree. F. and steamed for two hours at 1450.degree. F. is termed M activity. When the calcined sample is steamed at 1500.degree. F. for two hours, it is termed the S activity. When the calcined sample is first steamed for two hours at 1550.degree. F., it is termed S+ activity.
Prior art commercial catalyst formed from Y zeolites which had an Na content expressed as Na.sub.2 O based upon the volatile free zeolite of the order about 3 to 4% produced by exchanging with acid or ammonium or with rare earth or with rare earth and magnesium ions or with calcium ions and incorporated in a matrix composed of alumina and clay had characteristic M activities ranging from about 65 to about 80 for concentrations of the zeolite ranging from about 10% to 25% based upon the catalyst. The S+ activity of such catalysts were about 20% which is also substantially the S+ activity of the matrix. These values are not to be taken as characteristic of all prior art catalysts, but of the type which have been designated as B type catalysts. (See our copending Application, Ser. No. 782,971).
The need for catalysts of greater thermal and hydrothermal stability lead to the development of what has become known in this art as "ultra stable" catalyst. These catalysts employ Y zeolites which have been exchanged to reduce the Na.sub.2 O value to under 1%.
The S+ activity produced with such catalysts is indicative of a zeolite which is to a considerable degree hydrothermally stable. The activity of the catalyst after exposure of the calcined catalyst formulated from the zeolite to steam at 1550.degree. F. for two hours will show an S+ activity in the range of about 40 to 50% for concentrations while not necessarily that of all such ultra stable catalysts, such values are characteristic of what have been termed A type catalysts (See the above Application) ranging from about 15 to 25% in the catalyst composition.
The techniques for carrying out such exchanges in the prior art have been described in the prior art (see Rabo "Zeolite Chemistry and Catalysis", page 309 and 310 published by the American Chemical Society in 1976 and see also U.S. Pat. Nos. 3,293,194, 3,402,996, 3,867,277, 3,281,199, 3,169,692 and 3,463,608). And such procedure has also been reported when using an X type zeolite (see Pat. No. 3,966,882). The literature in this art is extremely voluminous and this statement of the art is not intended to be exhaustive but for the purposes of placing the present invention in the historical perspective of this art (see our copending application Ser. No. 718,167 filed Mar. 30, 1977). Applicants in the aboveidentified application discovered an improved method of reducing the sodium content of the faujasite type zeolites. The zeolites thus formed have Na.sub.2 O values of from about 2.5% to about 0.5% and catalysts formed from such zeolites employing the above matrixes have S+ activities in the range of about 50 to 60%. The preferred exchange cation was ammonium NH.sub.4. Catalysts of the above type are also referred to as A type catalysts (see application, Ser. No. 782,971).